某单位准备和一个体车主或一国营出租车公司中的一家签订月租车合同，设汽车每月行驶x千米，个体车主收费y₁元，国营出租车公司收费为y₂元，观察下列图象可知，当x____ 时，选用个体车较合算

I'm David．When I was 13,my parents decided that I should go to England to improve my English．I had never been to other countries before，so I felt a little worried．My parents prepared everything for my journey．My plane was due(预期)to leave at 9：30 a．m．and arrive in two hours．I phoned the English family who I would stay with and they told me they would wait for me at the airport(机场)．

Unluckily my plane to London was delayed (延误)．I tried to phone the English family again but I couldn't speak to them because they had already left home for the airport．

When I arrived in London．it was already 1：30p.m．I went to get my luggage(行李)but I couldn't find it．I became very worried．Luckily, the airport staff(工作人员)was very helpful and efficient．I didn't wait long-they found it 10 minutes later．

My English family were still waiting for me! I was so happy! Then my new life in London began．My English family were quite kind．I learned a lot of English because I spent most of the day talking in English．I played computer games with the little boy in my English family．I also taught him how to play chess．Sometimes I told him stories I learned from my family．

I missed my family during my stay in London．but I also feIt sad when my stay there came to an end．My English family held a party for me．I enjoyed it very much．I’ll never forget that summer in London! It is one of the most wonderful experiences I've ever had．

阅读材料并回答问题。

材料一：

材料二：参战各方伤亡情况统计

材料三：人类最可尊敬的高尚品格是通过战争而揭示和显露出来的。没有战争，世界将陷入自私自利之中……永久和平是一个梦，并且还不是一个美梦，而战争是上帝安排的世界秩序的一部分。在战争中得到发展的是人类的最高贵的美德，包括勇敢、克已、忠于职责，以及甘冒生命危险的自我牺牲。

——德军参谋总长毛奇

材料四：《罗素——爱因斯坦宣言》：“有鉴于在未来的世界大战核子武器肯定会被运用，而这类武器肯定会对人类的生存产生威胁，我们号召世界各政府体会并公开宣布它们的目的不能发展成世界大战，而我们号召它们。因此在解决它们之间的任何争执应该用和平手段。”